1. Field of the Invention
This invention relates to the field of data protection, and in particular to protecting data from illicit copying from a remote source.
2. Description of Related Art
The protection of data is becoming an increasingly important area of security. In many situations, the authority to copy or otherwise process information is verified by evaluating the encoding of copy-protected material for particular characteristics. For example, on copy-protected material may contain watermarks or other encodings that identify the material as being copy-protected, and also contains other encodings that identify whether this particular copy of the material is an authorized copy, and whether it can be copied again. For example, an authorized copy of content material may contain a robust watermark and a fragile watermark. The robust watermark is intended to be irremovable from the encoding of the content material. Attempting to remove the watermark causes damage to the content material. The fragile watermark is intended to be damaged when the content material is illicitly copied. For example, common fragile watermarks are damaged if the content material is compressed or otherwise altered. In this manner, content material that is compressed in order to be efficiently communicated via the Internet will be received with a robust watermark and a damaged fragile watermark. A content-processing device that is configured to enforce copy protection rights in this example will be configured to detect the presence of a robust watermark, and prevent the processing of the content material containing this robust watermark unless an appropriate fragile watermark is also present. The assumption being that compressed content represents an unauthorized transfer of copyrighted material.
The design of a watermarking encoding process and corresponding watermark detection involves a tradeoff among conflicting requirements. An ideal watermark should be undetectable during a conventional rendering of the content material, yet easily detectable by the watermark detector. As the watermark's detectability by the watermark detector increases, so too does its detectability during a conventional rendering; similarly, as the watermark's undetectability during a convention rendering decreases, so too does its undetectability by the watermark detector. Conventional watermarking processes are biased to assure that the watermarking process does not affect the quality of the rendering of the content material, often at the cost of reduced detectability by a watermark detector. That is, the likelihood of a watermark detector producing an erroneous decoding of a watermark, or failing to detect the watermark, is not insubstantial.
In the aforementioned use of both a robust watermark and a fragile watermark, each watermarking process must be designed within these conflicting tradeoff requirements, and each watermarking process must be configured to have a different susceptibility to damage. The robust watermark must be substantially undetectable by the conventional rendering process, yet also be robust enough to be recognizable after the watermarked material has been compressed and reformulated into a decompressed form. The fragile watermark must also be substantially undetectable by the conventional rendering process, yet also fragile enough so that a reformulation of the material causes damage to the fragile watermark. Additionally, each of the watermark processes must be configured so that they do not interfere with each other.